The present invention relates to phenolic foams prepared from resole resins. More particularly, the present invention relates to generally closed cell phenolic foams which are prepared from resole resins and which have a K-factor of less than about 0.22.
Phenol-aldehyde foams have been prepared for many years by a method which involves the addition of an acid catalyst to a liquid phenol-aldehyde resole resin. Polymerization of the resole resin commences very quickly following the addition of the acid catalyst. Inasmuch as the reaction is highly exothermic, the heat liberated by the reaction rapidly increases the temperature of the reaction mixture. The continuing increase in reaction temperature progressively increases the rate of polymerization. Accordingly, the reaction proceeds to completion very quickly. In fact, once initiated, the reaction is generally considered to be nearly impossible to control. The temperature of the reaction mixture increases sufficiently to cause the formation of enough steam from the water originally present in the resole resin and the water formed during reaction to foam the resin. The accompanying high reaction temperature causes the initially liquid resole resin to cure to a solid infusible state before the foam collapses. The phenol-aldehyde foam thus prepared has an open cell structure. The open cell structure does not provide for optimum properties with regard to thermal conductivity and resistance to moisture absorption. In addition it has been found that open cell phenol-aldehyde foam has a tendency to punk, that is, to continue to glow red hot and to smolder after high heat is applied and then removed. However, in general the open cell foam has excellent fire resistance and generates only a small amount of smoke when subjected to high temperatures.
In addition to the foregoing difficulties, it has been found that most known cellular materials produced from phenolic polymers exhibit an unsatisfactory thermal conductivity initially. Other known cellular materials produced from phenolic polymers exhibit an undesirable increase in thermal conductivity with time.
Accordingly, it is an object of the present invention to provide an improved closed cell phenol-aldehyde foam material substantially free of the disadvantages of prior foams.
Another object is to provide improved closed cell phenol-aldehyde resin foam material which exhibits a high closed cell content without adversely affecting friability, compressive strength and the low flammability characteristics of the material.